1. Field of the Invention
The invention relates to pipe racks of a type used in mobile earth drilling units of various kinds where individually stored pipes are connected in a drill string of several pipes for drilling operations.
2. Description of the Prior Art
A type of drilling equipment known as a blast hole drill is widely used in surface mining and quarrying operations. This equipment is typically mobile--being mounted on a vehicle that travels on crawlers. The vehicle has a cab for operating personnel and a housing for the machinery that drives the unit. A long, pivoting mast is disposed horizontally when the unit is on the move, and is set upright for vertical drilling operations. The mast carries a number of individually stored pipes arranged longitudinally therein. These pipes are connected one at a time in a drill string as a hole is being drilled.
Blast hole equipment is used in surface mining and quarrying operations to drill holes of moderate depth. Explosives are lowered to the bottom of these holes and detonated to break up rock and other hard earth formations. This permits the excavation of the material disintegrated by the blast and allows expansion of the area being mined or quarried.
In certain mining operations it becomes advantageous to position the mast at an angle, up to 30.degree., for example, to drill a hole at that angle. There is a problem, however, in connecting drill pipes to an angular drill string. If the drilling operation were conducted on the vertical, the top section of pipe would be suspended from a drill head and lowered to connect it at the end of the drill string that projects vertically upward from the hole. When drilling at an angle, a pipe that is connected at its upper end to the drill head will not be suitably supported at its lower end to permit alignment with, and a threading connection to, the drill string.
Pipes have been connected to the drill string with the aid of pipe handling mechanisms in which the pipes are stored. One such mechanism is shown and described in Reischl, U.S. Pat. No. 3,212,593, issued Oct. 19, 1965, and another is shown and described in Nelmark et al, U.S. Pat. No. 3,860,126, issued Jan. 14, 1975. In both of these, each pipe is stored in an individual pipe carrier with a socket at its lower end. In both of these, a pipe must be connected to the drill head, lifted clear of the socket and the pipe carrier must be retracted before the pipe can be connected to the drill string. Conversely, the pipe must be disconnected from the drill string before the pipe carrier can be moved out to receive the pipe. In angle drilling this results in the lower end of the pipe being unsupported by the carrier when being connected to the string, and just after disconnection from the drill string.